The active immunotherapy of a 3-methylcholanthrene-induced rat tumor with Friend virus-infected (xenogenized) tumor cells.

We investigated the various conditions necessary for potentiating the immunogenicity of viable Friend virus (FV)-infected rat fibrosarcoma KMT-17 cells. The immunogenicity was most potent among cells passaged through three generations of FV-tolerant rats; a single subcutaneous immunization induced an increase in the transplantation resistance (LTD50) of 10,000 or more. It was also found that intradermal immunization of the tumor cells induced stable and potent resistance to the transplantation of non-xenogenized tumor cells soon after immunization, and that irradiated non-xenogenized tumor cells were effective in supplying booster immunization. Active immunotherapy against KMT-17 cells pre-transplanted subcutaneously was carried out on the basis of the above findings with the results that the active anti-tumor immunization alone caused a complete regression in 30% of the tumor-burdened rats. These findings indicate the possibility of achieving active immunotherapy with xenogenized tumor cells.